A high performance magnet made of a Fe alloy powder includes FePt magnet made of FePt alloy. The FePt magnet has a high protection against corrosion and is a relatively strong magnet. However, because the FePt magnet uses expensive Pt, an application is limited.
Thus, tetrataenite, which is an ordered alloy (NiFe) of Ni:Fe=1:1 is expected as substitution of the FePt magnet. Tetrataenite has a high coercivity. Although normal NiFe alloy has a coercivity of less than or equal to 100 Nm, tetrataenite included in an iron meteorite has a high coercivity of 100 kA/m (see Kotsugi et al., Applied Physics Express 3 (2010) 013001).
Tetrataenite is included in a grain boundary layer in an iron meteorite and is generated at a very slow cooling speed of −10−6° C./year. Although tetrataenite has a crystal structure of face-centered tetragonal lattice (fct), a phase transition occurs at 320° C., and taenite in which an atomic arrangement of face-centered cubic lattice (fcc) is disordered is formed.
Recently, it has been reported that magnetic particles including tetrataenite and having a relatively high coercivity can be artificially composed by hydrogen reduction of nano-particles of compound oxide of Fe and Ni (see Okubo et al., Proceedings of Annual Meeting of Japan Society for Molecular Science 2011, 3P076). However, the magnetic particles have a coercivity of about one-third of tetrataenite included in an iron meteorite.
The inventor of the present application earnestly studied about artificial composition of magnetic alloy powder including an alloy of Fe and Ni and composed magnetic particles including tetrataenite at a temperature lower than or equal to 320° C. using amorphous compound hydroxide of Fe and Ni as source material and calcium hydride as reducing agent. However, the magnetic particles have a coercivity of one-fifth of tetrataenite included in an iron meteorite, that is, natural tetrataenite.